[aerandir92]

Kodi 18 is adding proper support for HDR video, and I've been using that for a while already, I'm loving it!
Also, playing SDR movies with HDR output also works fine (on Nvidia Shield), although not perfect, that might be the shields problem. 

But the opposite, playing HDR content on an SDR display, can look absolutely horrible. I did some comparisons with MPC-BE and Kodi 17 DSPlayer with MadVR, which both do a much better job at this.
The comparison is done with the Divergent Blu-ray (for SDR reference) and 4K Blu-ray for HDR to SDR conversion.

SDR Blu-ray reference




MPC-BE playing HDR on SDR screen




Kodi 17 DSPlayer with MadVR playing HDR on SDR screen



Kodi 18 playing HDR on SDR screen




While MPC-BE and DSPlayer is not equal to the SDR reference (and I think MadVR actually aims to not be equal, but better), they are clearly quite close to the reference, close enough that it doesn't matter. 
But Kodi 18 is just unusable. It looks so bad and blown out.

[Warner306]

There is a tone mapping parameter in the video settings menu that can be adjusted.

Not really a fair comparison given madVR is using much more expensive processing. Tone mapping requires heavy processing and Kodi needs to be fast. It difficult to get a perfect color match without having an expert on tone mapping on-hand at Team Kodi. It isn't as simple of a problem to solve as you might think. There is some complicated color science involved.

Try using the tone mapping parameter to see if you can rein in the brightness.

[jjd-uk]

Make sure Render method is set Pixel Shaders selected in Player -> Video

[ashlar]

Although I've been and still am a big fan of what madVR can do, I think HDR tone mapping makes the most of its sense when applied to projectors. If you don't have a HDR TV, watch SDR stuff. I don't own a HDR TV, in case somebody thinks I'm speaking from a privileged point of view.

[kaamaan]

For me Kodi conversion HDR to my SDR TV (LG) is incredibly dark. Is any way to fix that, please?

[kofii12345]

Same here

[kalima]

I have same issues with my OLED LG No HDR.

Kodi V18.1 + AMD Radeon RX570

[brazen1]

No dark issues here using a Samsung LCD.

[kofii12345]

Tof me that is Xiaomi box HDR->SDR issue. When I disable it Kodi wont convert the video. How to activate Kodi's HDR->SDR?

[albur]

Make sure Render method is set Pixel Shaders selected in Player -> Video

Where is that para meter? In render method it says auto detect but i can change it

[jjd-uk]

Assuming you've got a Windows device since this thread is in the Windows subforum and Pixel Shaders is a windows only render method.

[kofii12345]

Is there any method to get more contrast and saturation on HDR->SDR for mac and Android?

There is a comparision between VLC and Kodi and VLC i closer to proper image (although it is to dimmed):

Kodi


VLC